The present invention relates to a spark plug used for an internal combustion engine such as an automobile, and more particularly to an improvement in a resistance containing spark plug which functions to suppress a noise or jamming wave component generated at its spark discharge.
In order to lower the level of a noise wave component in a frequency region higher than 300 MHz, it is generally desirable to provide a resistance, in proximity to the spark gap of the spark plug, which acts to suppress noise current produced at the moment of its spark discharge. For this purpose, a resistance containing spark plug which is constructed to seal a resistance having a length longer than 7 mm in proximity to its spark gap between its spark rod electrode made of nickel alloy and its terminal rod specially disposed in the central through hole of an elongated hollow cylindrical ceramic insulator, was disclosed in the Japanese patent application Nos. 79130/71 and 42777/76 by the same assignee. The former was laid open as OPI No. 45725/73, and the latter was laid open on Oct. 22, 1977. The present inventor' experiments have proved that such a resistance containing spark plug enabled the noise level generated at the time of discharge to be greatly lowered, but was yet unsatisfactory.